Did you know that there are places where you can enjoy some peace and quiet? No, I’m not referring to your favourite spot in the park that’s just a short walk away from your home. I’m talking about a special space where you won’t be disturbed at all. Curious to know more? Then you need to find out what is an Anechoic Chamber!
Today’s subject may only be important to people who are studying acoustical engineering. However, I encourage any enthusiast to learn about it as well. I won’t go too deep into this topic, as the scientific principles behind it can be quite mind numbing (especially for me. Don’t laugh!). But I hope you will still have a basic understanding of it!
Anechoic Chamber – Is it Really That Quiet?
An anechoic chamber is a room that is specially designed to be insulated from external noises, and to also completely absorb reflections of either sound or electromagnetic waves. The term “anechoic” is derived from “an-echoic” which means non-reflective or non-echoing. Ultimately, these chambers simulate a quiet open-space of infinite dimension.
Originally, anechoic chambers were only utilized for acoustical purposes, where the reflections of a room is minimized. However, in recent times, rooms that are designed to reduce reflections and external noises in radio frequencies, have been used as testing areas for antennas, radars, or electromagnetic interference.
The sizes of these chambers can range anywhere from as small as a household microwave oven, to spaces as large as aircraft hangars. To determine the amount of space a chamber should have, designers will consider the sizes of the possible objects to be tested, and also take into account the frequency range of the signals used.
Here are the topics that we will be discussing further:
- Chamber acoustics
- Chamber wall function
- Semi-anechoic chambers
Acoustical experiments are often conducted in anechoic chambers because they are spaces with nominally “free field” conditions, which means that there will be no reflected signals. Almost all of the sound waves that are produced by the source, will not be reflected back. Common experiments include measuring the directivity of noise radiation from industrial machinery.
An anechoic chamber’s interior is very quiet, with typical noise levels ranging between 10 to 20 dBA. The best anechoic chamber in 2005, was able to achieve a measurement of −9.4 dBA. In 2015 however, an anechoic chamber that was built on the campus of Microsoft, broke the world record with a measurement of −20.6 dBA.
In general, the human ear can only detect sounds that are above 0 dBA. Hence, if a person were to be present in such a chamber, he would have the perception that the interior environment is devoid of sound. Based on personal accounts, some people may actually find such quietness to be very uncomfortable and disorienting.
Chamber Wall Function
The walls of an anechoic chamber plays a vital role in minimizing the reflection of sound waves. In the diagram (below), an incident sound wave I is about to impinge onto a wall with a series of wedges W with height H. After the impingement, the incident wave I is reflected as a series of waves R which in turn “bounce up-and-down” in the gap of air A, between the wedges W.
Due to the bouncing, a standing wave pattern may be produced in A (at least temporarily). At the same time this is occurring, the acoustic energy of the waves R gets dissipated via the air’s molecular viscosity, especially near the corner C. Furthermore, the foam materials used to fabricate the wedges causes another dissipation mechanism to occur during the wave/wall interactions.
Ultimately, the whole process will result in the component of the reflected waves R along the direction of I that escapes the gaps A (and goes back to the source of sound), denoted R’, to be notably reduced. Although this is a two-dimensional illustration, it is still an accurate representation of the actual three-dimensional wedge structures used in anechoic chambers.
Semi-anechoic chambers are designed to have a solid floor that acts as a platform where heavy objects such as cars, washing machines, or industrial machinery, are placed on. This is unlike full anechoic chambers (designed to absorb energy in all directions) where there is often a mesh floor grille that is layered over absorbent tiles.
Furthermore, in order to provide isolation from outside vibration or electromagnetic signals, the solid floor (used in semi-anechoic chambers) is damped and made to float on absorbent buffers. A professional recording studio may also integrate a semi-anechoic chamber to record music free of outside noise and unwanted reflections or reverberation.
That’s about all I have to share with you folks today. Have you ever been inside an anechoic chamber before? Would you enjoy the quietness?
Let me know your thoughts down below, and do share this article!